2153 - Dynamic Bowtie-Enhanced kV-MV Integrated Radiotherapy System: A Phantom Study for Simultaneous Imaging Quality Improvement and Dose Optimization
Presenter(s)
X. Lin1, Y. Zhang2, Y. Liu3, F. Yan4, J. Chen2, and Y. Yang5; 1Shanghai United Imaging Healthcare Advanced Technology Research Institute Co., Ltd., Shanghai, China, 2Department of Radiation Oncology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China, 3Shanghai United Imaging Healthcare Co., Ltd., Shanghai, China, 4Department of Radiology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China, 5Central Research Institute-Ruijin UIH Joint Research and Development Center, Ruijin Hospital, Shanghai Jiaotong University School of Medicine., Shanghai, China
Purpose/Objective(s): With the recently introduced fan beam CT guided radiotherapy (RT), onboard diagnostic quality CT becomes available to guide RT with the goal to achieve improved tumor localization accuracy and dose delivery precision. However, repeated high-quality CT acquisition inevitably increases radiation exposure to patients. This study proposes a novel dynamic bowtie-based kV-MV integrated radiotherapy strategy that optimizes CT imaging quality while minimizing additional organ dose exposure.
Materials/Methods: A custom-designed dynamic bowtie assembly comprising two adjustable wedge filters was implemented on onboard CT source. Through parametric optimization of inter-wedge spacing (0/5/10/15 mm), the system creates adaptive high-flux windows modulating kV dose for planning treatment volume (PTV) coverage and CT imaging field-of-view. A digital lung phantom with 27.6 cc spherical tumor was employed at mid left lung to validate the integrated kV-MV approach under 7-beam IMRT configuration. In our study, the prescription dose was 60 Gy in 30 fractions. The constraints are Dmax=66 Gy and V20Gy=37% for lungs and heart. To perform the kV-MV combined dose optimization, tube current of CT source, as well as the corresponding bowtie configuration, at each angle of CT projection were optimized along with the modulations of each MV IMRT beams. Spatialized signal to noise ratio of CT image was also considered as a term of optimization to achieve optimal CT image quality. The baseline IMRT plan employed conventional MV dose optimization with the same beam angles and adjusted prescription, where the PTV dose was set as original prescription subtracting conventional 100 mAs FBCT imaging dose.
Results: As compared to conventional 100mAs FBCT, the dynamic bowtie-enhanced kV image noise inside and 5 cm around PTV were reduced by 72.8% and 60.38%, which indicated significant improvement in image quality achieved by dynamic bowtie enhancement technique. Dose to the lungs and heart were all within constraints (Lung_Dmax = 65.93 Gy; Heart_Dmax = 58.47; Lung_V20Gy=8.45%, Heart_V20Gy=4.97%). The dose volume uniformity index (DVUI) is 1.24 for dynamic bowtie-enhanced kV-MV plan and 1.36 for baseline IMRT plan. Dynamic bowtie-enhanced kV-MV plan outperformed baseline IMRT in dose volume uniformity in PTV. The maximum dose to the lungs (not including GTV), skin and heart were comparable to the baseline IMRT plan with slight difference of -0.076%, 0.64% and 1.19% when implementing dynamic kV-MV dose planning. The mean dose to these organs were changed by 0.00%, 1.30%, 0.42%, respectively, as compared to baseline IMRT.
Conclusion: This proof of concept study demonstrates the feasibility of dynamic bowtie technology for synergistic imaging quality and treatment dose optimization for a kV-MV treatment strategy, paving the way for more accurate RT without needing to consider the excessive radiation dose caused by high-quality onboard CT acquired on a per-fraction basis or even per-beam/arc basis.